Amblyopia, more commonly known as `lazy eye`, refers to a condition where young children develop decreased vision in one or both eyes. In amblyopia, the structural integrity of the eye is usually normal. However, in many cases children develop amblyopia because of a large difference in the focusing power between the two eyes. This type of amblyopia is often referred to by ophthalmologists as anisometropic amblyopia because it is caused by the difference in the refraction between each eye.
Amblyopia affects up to 4 percent of all children in the United States. However, it is amenable to treatment with early diagnosis. To properly treat a child for amblyopia, it is very important to make the diagnosis and initiate treatment when the child is very young. Often times, however, the diagnosis of amblyopia will not be made until the vision in one eye deteriorates to the point that one eye pivots inwardly or outwardly. This visual defect is termed strabismus, and is commonly referred to in the lay literature by the term `lazy eye`. Unfortunately, when turning of an eye occurs, it is often difficult to correct the problem, and only partial success is normally achieved.
With normal vision, both eyes will `aim` at the same points of interest, and the brain will then combine the `picture` taken by each eye into a single three-dimensional image. This three-dimensional image is what allows one to have depth perception. However, when one eye turns, two different `pictures` are sent to the brain, and in a child, the brain learns to ignore the image of the misaligned eye and sees only the image from the straight or better seeing eye, and this results in a loss of depth perception, and ultimately loss of vision in the deviating eye. This loss of vision is often permanent, and may render the patient legally blind in the affected eye.
In view of the frequency of this problem, and the need for this condition to be detected early in order for the patient to have the greatest chance of total vision correction [see J Ophthalmic Nurs Technol 17(6):227 (1998), Can Fam Physician 44:337 (1998), and Pediatr Clin North Am 45(4):993 (1998)] pediatricians and school nurses often screen children for amblyopia at between 3 and 4 years of age. Screening programs utilizing conventional materials and protocols such as Snellen charts and retinoscopy are highly successful in identifying children who are at risk for amblyopia. However, treatment is complicated by the fact that the children are often uncooperative or do not understand the examination techniques. In order to prescribe glasses for a young child it is necessary to evaluate the light reflex which comes off the retina. This is normally accomplished by a retinoscopic examination that allows for light reflexes coming off of the retina to be examined and thereby determine the refractive state of the eye. The ophthalmologist or other licensed professional can then prescribe glasses for the patient as needed. However, this technique is difficult to perform in children less than 4 years of age because they are often frightened of the device and do not want the ophthalmologist, pediatrician, nurse or other licensed professional to hold lenses or examination instruments close to their eyes. The use of a retinoscope is absolutely necessary in order to rule out amblyopia in very young children less than 4 years of age.
Prior attempts to attract, maintain and fix the gaze of a patient during an ophthalmic examination have included such devices as a small animatable fixation target, such as a small toy animal with movable body parts, that is held in the mouth of the licensed professional in front of the patient undergoing the ophthalmic examination. Such a device, as described in U.S. Pat. No. 4,093,359, for example, is obviously unsatisfactory and cumbersome for the licensed professional.
Other attempts to provide fixation devices for patients also exhibit limitations. For example, a rotatable disk upon which is drawn a downward spiral and will draw the observer's attention to the center of the spiral when rotated, or mechanical figures that are capable of movement when activated may also be used as fixation devices for patients, especially young children, undergoing ophthalmologic examinations. However, such devices normally require that they be mounted behind the licensed professional; are fairly large; and are difficult for the licensed professional to operate and control during the examination.